1. Field of Invention
The present invention relates to a method of preparing ethylene glycol from cellulose, and more particularly to a reaction process of cellulose under hydrothermal condition, wherein the cellulose reaction process of the method comprises catalytic degradation and hydrogenation reactions.
2. Description of Related Arts
The ethylene glycol is one of liquid fuels, and also is an important feed for polyester synthesis. For examples, the ethylene glycol can be used for synthesizing polyethylene terephthalate (PET), and polyethylene naphthalene (PEN); the ethylene glycol can also be used as antifreeze agents, lubricant, plasticizers, or surfactant etc. Thus, the ethylene glycol has variety of applications in the organic chemical material.
At present, the industrial process for producing the ethylene glycol is consuming petroleum resources as the raw material, wherein the ethylene glycol is produced via oxidizing ethylene to form epoxyethane, and then hydrating it to obtain the ethylene glycol. (Literature 1: CUI Xiao-ming, the overview of the production development of ethylene glycol, Chemical Industry, 2007, 25, (4), 15-21. Literature 2: Process for preparing ethanediol by catalyzing epoxyethane hydration, Patent No. CN1463960-A; Patent No. CN1204103-C). The conventional method for ethylene glycol production is based on the nonrenewable petroleum sources, and involving the oxidization or epoxidation process, which comprises complicated reaction steps, so that the procedure of preparing ethylene glycol is low efficient, containing high amount of undesired side products, consuming much energy, and causing serious pollutions.
Therefore, finding renewable materials for producing ethylene glycol is able to reduce the dependence on the petroleum, so as to build an eco friendly manufacturing process. Currently, the researches of converting the biomass into ethylene glycol are mostly focusing on starch, glucose, sucrose, and sugar alcohols, such as hexitols, as the raw materials for the conversion therefrom. (Literature 3: Process for the preparation of lower polyhydric alcohols, U.S. Pat. No. 5,107,018. Literature 4: Preparation of lower polyhydric alcohols, U.S. Pat. No. 5,210,335). However, the above mentioned raw materials for the conversion of ethylene glycol are the currently basic food of human beings, so that using them for ethylene glycol production is facing the dilemma of mankind survival and development. Cellulose is the largest renewable resources having rich sources, such as the remaining straw from the agricultural production or the wastes from the forestry, etc., which are low in cost for using as the raw material for the conversion of biomass. Using cellulose for synthesizing ethylene glycol can not only build up a new synthesis process to achieve low cost, but also obtain the high value product of the ethylene glycol. Furthermore, the cellulose is unable to be digested by human beings, so that using the cellulose as the raw material for the ethylene glycol production will not affect the food security and not reduce the food production for the mankind. In addition, the cellulose is formed by the condensation of glycosidic bond of glucose units containing a large number of hydroxyls. Those hydroxyls are fully reserved during the process of cellulose converting into ethylene glycol, which makes the conversion process has a very high atom economy. Therefore, the process of converting cellulose into ethylene glycol has significant advantages over most of the existing processes of making ethylene glycol.
Though there are numbers of advantages of producing polyols from cellulose, cellulose contains a large amount of intermolecular and intramolecular hydrogen bonds, so that the structure of cellulose is very robust. Therefore, the cellulose is usually first hydrolyzed to reducing sugar by acids, and then the obtained glucose is further converted for other uses. The whole process is not only complicated, but also generates the environmental pollution issues. (Literature 4: Two stage hydrogenolysis of carbohydrate to glycols using sulfide modified ruthenium catalyst in second stage, U.S. Pat. No. 4,476,331). The present invention provides a reaction process, which is using water, the most environmental friendly solvent, as the reaction medium, is no need of adding acid or base, and is able to be completed via one step to accomplish the high yield of ethylene glycol from cellulose.